/*
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */
 
/* $Id: iconvme.c 3 2007-07-10 06:59:05Z kf701.ye $ */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <iconv.h>
#include <limits.h>

#ifndef SIZE_MAX
# define SIZE_MAX ((size_t) -1)
#endif

/**
 * @brief codeset convert
 *
 * Convert a zero-terminated string STR from the FROM_CODSET code set
 * to the TO_CODESET code set.  The returned string is allocated using
 * malloc, and must be dellocated by the caller using free.  On
 * failure, NULL is returned and errno holds the error reason.  Note
 * that if TO_CODESET uses 0 for anything but to terminate the
 * string, the caller of this function may have difficulties finding
 * out the length of the output string.
 *
 * @param str  raw buffer need convert
 * @param from_codeset such as "gbk"
 * @param to_codeset such as "utf-8"
 *
 * @return the converted buffer or NULL when faild
 * you must free the retval buffer yourself
 *
 */
char *iconv_string (const char *str, const char *from_codeset,
		const char *to_codeset)
{
	char *dest = NULL;
	iconv_t cd;
	char *outp;
	char *p = (char *) str;
	size_t inbytes_remaining = strlen (p);
	/* Guess the maximum length the output string can have.  */
	size_t outbuf_size = inbytes_remaining + 1;
	size_t outbytes_remaining;
	size_t err;
	int have_error = 0;

	/* Use a worst-case output size guess, so long as that wouldn't be
	   too large for comfort.  It's OK if the guess is wrong so long as
	   it's nonzero.  */
	size_t approx_sqrt_SIZE_MAX = SIZE_MAX >> (sizeof (size_t) * CHAR_BIT / 2);
	if (outbuf_size <= approx_sqrt_SIZE_MAX / MB_LEN_MAX)
		outbuf_size *= MB_LEN_MAX;
	outbytes_remaining = outbuf_size - 1;

	if (strcmp (to_codeset, from_codeset) == 0)
		return strdup (str);

	cd = iconv_open (to_codeset, from_codeset);
	if (cd == (iconv_t) -1)
		return NULL;

	outp = dest = (char *) malloc (outbuf_size);
	if (dest == NULL)
		goto out;

again:
	err = iconv (cd, &p, &inbytes_remaining, &outp, &outbytes_remaining);

	if (err == (size_t) - 1)
	{
		switch (errno)
		{
			case EINVAL:
				/* Incomplete text, do not report an error */
				break;

			case E2BIG:
				{
					size_t used = outp - dest;
					size_t newsize = outbuf_size * 2;
					char *newdest;

					if (newsize <= outbuf_size)
					{
						errno = ENOMEM;
						have_error = 1;
						goto out;
					}
					newdest = (char *) realloc (dest, newsize);
					if (newdest == NULL)
					{
						have_error = 1;
						goto out;
					}
					dest = newdest;
					outbuf_size = newsize;

					outp = dest + used;
					outbytes_remaining = outbuf_size - used - 1;	/* -1 for NUL */

					goto again;
				}
				break;

			case EILSEQ:
				have_error = 1;
				break;

			default:
				have_error = 1;
				break;
		}
	}

	*outp = '\0';

out:
	{
		int save_errno = errno;

		if (iconv_close (cd) < 0 && !have_error)
		{
			/* If we didn't have a real error before, make sure we restore
			   the iconv_close error below. */
			save_errno = errno;
			have_error = 1;
		}

		if (have_error && dest)
		{
			free (dest);
			dest = NULL;
			errno = save_errno;
		}
	}
	return dest;
}
